Pet tracer for imaging of neuroendocrine tumors

ABSTRACT

There is provided a radiolabelled peptide-based compound for diagnostic imaging using positron emission tomography (PET). The compound may thus be used for diagnosis of malignant diseases. The compound is particularly useful for imaging of somatostatin overexpression in tumors, wherein the compound is capable of being imaged by PET when administered with a target dose in the range of 150-350 MBq, such as 150-250 MBq, preferable in the range of 191-210 MBq.

This application is a National Stage Application of PCT/DK2012/050305,filed 23 Aug. 2012, which claims benefit of Serial No. PA 2011 00654,filed 31 Aug. 2011 in Denmark, and claims benefit of U.S. ProvisionalSer. No. 61/529,262, filed 31 Aug. 2011, and which applications areincorporated herein by reference. To the extent appropriate, a claim ofpriority is made to each of the above disclosed applications.

FIELD OF THE INVENTION

The present invention relates to a radiolabelled peptide-based compoundfor diagnostic imaging using positron emission tomography (PET). Thecompound may thus be used for diagnosis of malignant diseases.

BACKGROUND OF THE INVENTION

Known imaging techniques with tremendous importance in medicaldiagnostics are positron emission tomography (PET), computed tomography(CT), magnetic resonance imaging (MRI), single photon computedtomography (SPECT) and ultrasound (US). Although today's imagingtechnologies are well developed they rely mostly on non-specific,macroscopic, physical, physiological, or metabolic changes thatdifferentiate pathological from normal tissue.

Targeting molecular imaging (MI) has the potential to reach a newdimension in medical diagnostics. The term “targeting” is related to theselective and highly specific binding of a natural or synthetic ligand(binder) to a molecule of interest (molecular target) in vitro or invivo.

MI is a rapidly emerging biomedical research discipline that may bedefined as the visual representation, characterization andquantification of biological processes at the cellular and sub-cellularlevels within intact living organisms. It is a novel multidisciplinaryfield, in which the images produced reflect cellular and molecularpathways and in vivo mechanism of disease present within the context ofphysiologically authentic environments rather than identify molecularevents responsible for disease.

Several different contrast-enhancing agents are known today and theirunspecific or non-targeting forms are already in clinical routine. Someexamples listed below are reported in literature.

For example, Gd-complexes could be used as contrast agents for MRIaccording to “Contrast Agents I” by W. Krause (Springer Verlag 2002,page one and following pages). Furthermore, superparamagnetic particlesare another example of contrast-enhancing units, which could also beused as contrast agents for MRI (Textbook of Contrast Media,Superparamagnetic Oxides, Dawson, Cosgrove and Grainger Isis MedicalMedia Ltd, 1999, page 373 and following pages). As described in ContrastAgent II by W. Krause (Springer Verlag 2002, page 73 and followingpages), gas-filled microbubbles could be used in a similar way ascontrast agents for ultrasound. Moreover “Contrast Agents II” by W.Krause (Springer Verlag, 2002, page 151 and following pages) reports theuse of iodinated liposomes or fatty acids as contrast agents for X-Rayimaging.

Contrast-enhancing agents that can be used in functional imaging aremainly developed for PET and SPECT.

The application of radiolabelled bioactive peptides for diagnosticimaging is gaining importance in nuclear medicine. Biologically activemolecules which selectively interact with specific cell types are usefulfor the delivery of radioactivity to target tissues. For example,radiolabelled peptides have significant potential for the delivery ofradionuclides to tumours, infarcts, and infected tissues for diagnosticimaging and radiotherapy.

DOTA (1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10tetraazacyclododecane)and its derivatives constitute an important class of chelators forbiomedical applications as they accommodate very stably a variety of di-and trivalent metal ions. An emerging area is the use of chelatorconjugated bioactive peptides for labeling with radiometals in differentfields of diagnostic and therapeutic nuclear oncology.

There have been several reports in recent years on targeted radiotherapywith radiolabeled somatostatin analogs.

US2007/0025910A1 discloses radiolabled somatostatin analogs primarilybased on the ligand DOTA-TOC. The radionucleotide can be (64)Copper andthe somatostatin analog may be octreotide, lanreotide, depreotide,vapreotide or derivatives thereof. The compounds of US2007/0025910A1 areuseful in radionucleotide therapy of tumours.

US2007/0025910A1 does not disclose (64)Cu-DOTA-TATE. DOTA-TATE andDOTA-TOC differ clearly in affinity for the 5 known somatostatinreceptors (SST1-SST2). Accordingly, the DOTA-TATE has a 10-fold higheraffinity for the SST2 receptor, the receptor expressed to the highestdegree on neuroendocrine tumors. Also the relative affinity for theother receptor subtypes are different. Furthermore, since 177Lu-DOTATATEis used for radionuclide therapy, only 64Cu-DOTATATE and not64Cu-DOTATOC can be used to predict effect of such treatment by a priorPET scan.

There exists a need for further peptide-based compounds having utilityfor diagnostic imaging techniques, such as PET.

SUMMARY OF THE INVENTION

The present invention is based on the use of the compound ⁶⁴Cu-DOTA-TATEhaving the formula:

as a PET tracer for better imaging of neuro-endocrine tumors.

The present inventors have surprisingly found that this compound orligand works better (higher resolution/image quality) than similaranalogues for specific PET imaging of somatostatin-expressing tumors(neuroendocrine tumors). Especially, the inventors have found thecompound is particularly useful for diagnostic use, when the compound isadministered with a target dose in the range of 150-350 MBq, such as150-250 MBq. The compound is very useful for in vivo diagnosis orimaging, for example by PET, of a neuroendocrine tumor, when thecompound is administered with a target dose in the range of 191-210 MBq.This target dose cannot be determined without conducting severalclinical trials in human; animal models are not suitable to find thistarget dose.

The invention also provides use of the compound or a pharmaceuticallyacceptable salt thereof for the manufacture of a composition for use ina radiographic imaging method, wherein cells or tissues are contactedwith the compound; and a radiographic image is made. Preferably, thecompound is detected by a gamma camera, positron emission tomography(PET) or single photon emission tomography (SPECT), wherein the compoundis administered with a target dose in the range of 150-350 MBq, such as150-250 MBq, preferable in the range of 191-210 MBq.

The present invention also provides use of the compound or apharmaceutically acceptable salt thereof in the preparation of acomposition for detection of a tumor, tumor tissue, cancer or metastasisin a subject, wherein the compound is administered with a target dose inthe range of 150-350 MBq, such as 150-250 MBq. Preferably, the compoundof the present invention is used for the manufacture of aradiopharmaceutical for use in a method of in vivo imaging, wherein thecompound is administered with a target dose in the range of 191-210 MBq.

In another aspect the present invention provides a method for imaging ofsomatostatin overexpression in tumors or other tissues comprisingadministering a compound of the present invention or a pharmaceuticallyacceptable salt thereof to a subject, wherein the compound is capable ofbeing imaged by PET, detecting somatostatin overexpression in tumors byperforming PET, wherein the compound is administered with a target dosein the range of 150-350 MBq, such as 150-250 MBq, preferable in therange of 191-210 MBq.

In still another aspect the present invention provides a method ofgenerating an image of a human body comprising administering a compoundof the present invention or a pharmaceutically acceptable salt thereofto said body and generating an image of at least a part of said body towhich said compound has distributed using PET, wherein the compound isadministered with a target dose in the range of 150-350 MBq, such as150-250 MBq, preferable in the range of 191-210 MBq.

There is also provided a method of monitoring the effect of treatment ofa human body with a drug to combat a condition associated with cancer,preferably a neuroendocrine tumor, said method comprising administeringto said body a compound of the present invention or a pharmaceuticallyacceptable salt thereof and detecting the uptake of said compound bycell receptors, wherein the compound is administered with a target dosein the range of 150-350 MBq, such as 150-250 MBq, preferable in therange of 191-210 MBq.

Additionally, there is provided a method of radiotherapy for thetreatment of solid tumors comprising: administering to a mammalharboring a solid tumor, preferably a neuroendocrine tumor, in need ofsaid treatment, an effective dose of a compound of the present inventionor a pharmaceutically acceptable salt thereof.

Finally, there is provided a method for manufacturing a compound ofFormula I

said method comprising the steps:

-   -   Mixing DOTA-TATE under presence of a scavenger, such as gentisic        acid. with a water soluble ⁶⁴Cu-salt in an acidic aqueous        solution;    -   Leaving the solution for at least 2 min;    -   Passing the solution through a sterile filter; and    -   Recovering the filtered material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 show PET scans of a patient with intense bowel activity (leftlower abdomen).

FIG. 2 shows PET scans of patient with metastasis.

FIG. 3 shows a pancreatic lesions on a ⁶⁴Cu-DOTA-TATE PET-CT and on anequivalent contrast enhanced late arterial phase-CT slice obtained 12months later.

FIG. 4 shows scans of the same cancer patient with neuroendocrinetumors. Left the current gold-standard (111In-octreotide) and right64-Cu-DOTATATE.

DETAILED DESCRIPTION OF THE INVENTION

The invention is now explained in more detail based on an example.Further details may be found in THE JOURNAL OF NUCLEAR MEDICINE⋅Vol.53⋅No. 8⋅August 2012 Vol. 53, No. 8, August 2012, which is herewithincorporated by reference.

Before explaining the below experimental evidence in more detail itshould be noted that the inventors have now clinically tested the⁶⁴Cu-Dotatate-DOTA-TATE complex of the present invention on more than120 patients with similar results as described below.

EXAMPLE

Preparation of ⁶⁴Cu-Dotatate-DOTA-TATE

⁶⁴Cu was produced using a GE PETtrace cyclotron equipped with abeamline. The ⁶⁴Cu was produced via the ⁶⁴Ni (p,n) ⁶⁴Cu reaction using asolid target system consisting of a water cooled target mounted on thebeamline. The target consisted of ⁶⁴Ni metal (enriched to >99%)electroplated on a silver disc backing. For this specific type ofproduction a proton beam with the energy of 16 MeV and a beam current of20 uA was used. After irradiation the target was transferred to thelaboratory for further chemical processing in which the ⁶⁴Cu wasisolated using ion exchange chromatography. Final evaporation from aq.HCl yielded 2-6 GBq of ⁶⁴Cu as ⁶⁴CuCl2 (specific activity 300-3000TBq/mmol; RNP >99%). The labeling of ⁶⁴Cu to DOTA-TATE was performed byadding a sterile solution of DOTA-TATE (0.3 mg) and Gentisic acid (25mg) in aq Sodium acetate (1 ml; 0.4M, pH 5.0) to a dry vial containing64CuCl2 (˜1 GBq). Gentisic acid was added as a scavenger to reduce theeffect of radiolysis. The mixture was left at ambient temperature for 10minutes and then diluted with sterile water (1 ml). Finally, the mixturewas passed through a 0.22 μm sterile filter (Millex GP, Millipore).Radiochemical purity was determined by RP-HPLC and the amount ofunlabeled 64Cu2+ was determined by thin-layer chromatography. Allchemicals were purchased from Sigma-Aldrich unless specified otherwise.DOTA-Tyr3-Octreotate (SEQ ID NO: 1) (DOTA-TATE) was purchased fromSachem (Torrance, Calif.). Nickel-64 was purchased in +99% purity fromCampro Scientific Gmbh. All solutions were made using Ultra pure water(<0.07 μSimens/cm). Reversed-phase high pressure liquid chromatographywas performed on a Waters Alliance 2795 Separations module equipped withat Waters 2489 UV/Visible detector and a Caroll Ramsey model 105 S-1radioactivity detector—RP-HPLC column was Luna C18, HST, 50×2 mm, 2.5μm, Phenomenex. The mobile phase was 5% aq. acetonitrile (0.1% TFA) and95% aq. acetonitrile (0.1% TFA).

Thin layer chromatography was performed with a Raytest MiniGita StarTLC-scanner equipped with a Beta-detector. The eluent was 50% aqmethanol and the TLC-plate was a Silica60 on Al foil (Fluka). Ionexchange chromatography was performed on a Dowex 1×8 resin(Chloride-form, 200-400 mesh).

Patients and Inclusion Criteria

Fourteen consecutively enrolled patients participated in this pilotstudy and underwent PET scanning with the new tracer on several timepoints. Patients were eligible in case of a histopathologicallyconfirmed neuroendocrine tumor including positive immunostainings forchromogranin A and synaptophysin. They got offered study inclusion incase of referral to conventional SRI as part of routine follow-up. Themaximum allowed time interval between both imaging modalities was 60days. According to local clinical routine there was no need forinterruption of biotherapy e.g. withdrawal of long- or short-time actingsomatostatin analogs. However, patients must not have undergone majorsurgical interventions or systemic chemotherapy between conventional SRIand the PET scanning. The study group consisted of thirteen patientswith gastroenteropancreatic neuroendocrine tumors (2 foregut, 6 midgut,5 NET of unknown origin) and one patient with a known mutation in themultiple endocrine neoplasia I gene, who was diagnosed with abronchogenic NET ten years ago. Age ranged from 40-80 years. Genderdistribution: four women, ten men. Ten of the tumors were activefunctioning causing classical carcinoid syndromes mainly due to hepatictumor load. One patient had shown clinical and biochemicalmanifestations of a Zollinger-Ellison syndrome at time of diagnosis.Twelve patients were in advanced disease state—TNM stage IV according tomost recently both UICC/AJCC and ENETS classifications. Two patients hadundergone respectively R0- and R1-resections, both without detectabledisease so far. Supplementary patient characteristics are given inTable 1. Patient recruiting and follow-up was carried out at theDepartment of Abdominal Surgery C. SRI was performed at the Departmentof Clinical Physiology, Nuclear Medicine and PET. Both departments arepart of the Neuroendocrine Tumor Center of Excellence, Rigshospitalet,University of Copenhagen, Denmark. All patients had given writteninformed consent prior to inclusion. The study was approved by theDanish Medicines Agency and the Regional Research Ethics Committee.

TABLE 1 Patient Characteristics Age at study Time since Primary Ki67Patient No. Primary Sex inclusion (y) diagnosis (mo) resected?percentage Syndrome TNM* Metastases ¹⁸F-FDG 1 Cecum M 56 195 Yes NotCarcinoid IV Carcinomatosis Positive performed 2 Duodenum F 50 97 Yes 1Gastrinoma R0 Negative 3 CUP M 44 16 No 5 Carcinoid IV Peritoneum Notperformed 4 Ileum M 62 9 Yes 3 None R1 Not performed 5 Ileum M 63 88 Yes3 Carcinoid IV Lymph nodes Negative 6 CUP F 40 23 No 5 Carcinoid IVLiver Negative 7 Pancreas M 72 2 No 7 None IV Liver, bones Not performed8 Lower small F 51 92 Yes 3 Carcinoid IV Liver, breasts Negativeintestine 9 CUP M 81 3 No 10 Carcinoid IV Liver, peritoneum Positive 10Ileum M 64 10 Yes 1 None IV Lymph nodes Not performed 11 CUP M 84 38 No4 Carcinoid IV Liver Positive 12 Ileum M 72 6 No 10 Carcinoid IV Liver,bones, Not lymph nodes performed 13 Bronchogenic F 44 103 No 5 CarcinoidIV Lungs, lymph Positive NET nodes 14 CUP M 76 3 No 7 Carcinoid IV LiverPositive *TNM stage before study inclusion according to most recentclassifications of European Neuroendocrine Tumor Society and AmericanJoint Committee on Cancer/International Union Against Cancer. R0resection = complete resection, no microscopic residual tumor: CUP =cancer of unknown primary. R1 resection = microscopic residual tumor.

Image Acquisition

Patients received a target dose of 200 MBq ⁶⁴Cu-DOTATATE (range 191-210MBq). PET-CT images were acquired on an integrated PET-CT SiemensBiograpgh True X, multi-slice. Patients underwent PET scans on at leasttwo times after application of a mean dose of ⁶⁴Cu-DOTATATE via ananticubital vene. Imaging was performed 1 h, 3 h and 24 h afterinjection.

¹¹¹In-pentreotide was intravenously applied with a target dose of 200MBq. The scans consisted of whole body planar scintigraphy and SPECT-CT:Planar images were acquired at 24 h (anterior and posterior whole-bodyscan, scan speed 5 cm/min, 512*1.024 matrix) and at 48 h (15 min staticplanar image (256*256 matrix) of the abdomen using a large field of viewmedium-energy collimator (Precedence 16-slice scanner, PhilipsHealthcare; VG Hawkeye, GE Healthcare). SPECT (20 sec/step, 128 angles,128*128 matrix) over the abdomen was obtained at 24 or 48 h, andincluded also the chest if a pathological focus was suspected from thewhole body scan. A low-dose CT was used as anatomical guide and forattenuation correction. SPECT and CT were fused and reviewed ondedicated workstations (EBW, Philips Healthcare; eNTEGRA, GE Healtcare).

Image Analysis

Planar whole-body scans/ SPECT-CT and PET-CT images were evaluated bytwo separate teams consisting of both a nuclear medicine physician and aradiologist. Both teams were briefed about the patients past medicalhistory. When abnormal findings only detected on co-registered CT hadled the attention to a specific anatomical site, this particular regionwas revaluated using the molecular imaging data. Judged visually, therealso had to be clearly detectable lesion to be accounted as true SRIpositive as this was the main focus of interest of the present study.However, all lesions were documented, whether identified on CT images orby SRI. Findings were reported according to their respective anatomicalsite and if possible absolute numbers of lesions per organ system. All⁶⁴Cu-DOTATATE PET scans where supplemented with contrast enhancedhigh-dose CT, whereas half of all ¹¹¹In-pentreotide SPECT scans werecarried out for reasons of radioprotection by only using low-dose CTexcept if a contrast-enhanced diagnostic CT was ordered by the referringphysician. While still remaining blinded to the opposite SRI results,this disparity was tried to balance by additionally providing the teamevaluating ¹¹¹In-pentreotide SPECT-CT scans with the findings fromcontrast enhanced diagnostic CT. Interpretation of conventional SRI wasperformed based on the knowledge of normal tissue accumulation of¹¹¹In-pentreotide. Interpretation of the findings from the new PETmethod was carried out in a similar manner being aware of possibledifferences regarding residence times and excretion patterns of the newtracer. Confirmation of the pointed-out lesions was sought by routinefollow-up including CT, MRI, conventional SRI and biopsy if possible.Newly detected lesions on co-registered CT imaging were accepted forconfirmations as well. Semi-quantitative analysis of tissueradioactivity concentrations was performed by drawing volumes ofinterests (VOI) around detected lesions and encompassing normal tissueswith appreciable tracer uptake on fused PET-CT images. Standardizeduptake values (SUV) were automatically calculated and reported only forthose lesions with the highest tracer uptake per organ system (includingbone and lymph node lesions). SUV_(MAX) is considered a quitereproducible and convenient method for quantitative analysis of PETdata. However, this approach is based on SUV calculation consideringonly the highest image pixel of the target area and might not reflectthe normal/average distribution of somatostatin receptors within therespective organ. Moreover, it might be easily biased by erroneousinvolvement of adjacent tissue with high tracer uptake. We thereforealso generated SUV_(0.5MAX) values.

Dosimetry

Radiochemistry and Toxicity

The labeling of 64Cu-DOTATATE took less than 30 min and resulted ingreater than 95% yield, as shown with radio-RP-HPLC. No additionalradiochemical purification step was required. The amount of unlabeled64Cu in the product was less than 1%, as demonstrated by radio-TLC. Thespecific activity of 64Cu-DOTATATE was 4.78 MBq/mmol. The mean 6 SD ofthe administered mass of 64Cu-DOTATATE was 33.9 6 1.7 ng (range,31.7-38.0 ng). The mean administered activity was 207 6 10 MBq (range,193-232 MBq). There were no adverse or clinically detectablepharmacologic effects in any of the 14 subjects, except for 4 whoexperienced self-limiting nausea of seconds to a few minutes durationimmediately after injection. This side effect was probably due to thesomatostatin analog contained in the tracer. No significant changes invital signs were observed.

Biodistribution of 64Cu-DOTATATE

A characteristic imaging series illustrating activity biodistribution at1, 3, and 24 h after injection is shown in FIG. 1. On the basis of SUVquantitation, tracer accumulation was classified in the following 3categories: high, moderate, and faint. High accumulation of64Cu-DOTATATE was seen in the pituitary (averaged SUVmax 6 SEM at 1 hand 3 h, 19.0 6 2.6 and 19.4 6 3.3, respectively), adrenal glands (21.16 3.1 and 27.8 6 3.6, respectively), kidneys (21.3 6 2.5 and 19.9 6 2.0,respectively), renal pelvis, and urinary bladder. Moderate to highuptake was observed in the liver (11.3 6 0.8 and 13.6 6 0.8,respectively) and spleen (17.8 6 1.8 and 18.0 6 1.8, respectively). Thesalivary glands showed faint to moderate uptake in 12 of 14 patients. In2 patients, moderate tracer accumulation was observed in the thyroidgland, with a diffuse distribution pattern in one patient and a focalpattern in the other. In most patients, numerous lesions were clearlydelineated from surrounding tissue (background), showing tracer uptakeranging from moderate to intense (SUVmax range at 1 h and 3 h: liverlesions, 20-81 and 26-81, respectively; bone lesions, 30-117 and 27-111,respectively; and lymph nodes, 9-110 and 9-115, respectively). The TBRswere correspondingly high (1 h and 3 h: liver lesions, 2:1 and 7:1,respectively; bone lesions, 4:1 and 8:1, respectively; and lymph nodes,3:1 and 19:1, respectively). Background reference SUVmax for lymph nodeswas calculated from VOIs drawn over the lumbar part of the psoas muscle,and reference SUVmax for bones was generated by drawing VOIs overcontralateral or adjacent normal bone. SUVmax of the early and delayedimages remained relatively stable (variability #20%) for tissues thathad known high physiologic somatostatin receptor density and did nottake part in tracer or activity excretion (i.e., pituitary, adrenals,and spleen). The same was true for most lesions. Conversely, highertime-dependent intrapatient variability for SUVmax was observed for thekidneys, corresponding with urinary tracer excretion as demonstrated byactivity accumulation in the renal pelvis and urinary bladder seen onlyon the early and delayed images. As a possible sign of hepatobiliaryexcretion, an increase in SUVmax from the 1 h to the 3 h scan in normalliver tissue ranged from 10% to 65% among patients. This finding was inline with visible activity localized to the gallbladder on 3 h images,which was not apparent on images from the early acquisition.

Images of the late scan (24 h) were characterized by activity washoutfrom most organs and lesions, whereas activity retention in the liverand activity accumulation in the intestines became apparent. No activitywas visible in the renal collecting system or urinary bladder at thelate time point.

Table 2 depicts normalized cumulated activity for source organs. Table 3shows the associated absorbed dose estimates based on an estimatedurinary excretion fraction of 10%, with a presumed 2-h voiding intervaland a biologic half-life of 1 h. The dose calculations yielded aneffective dose of 0.0315 mSv/MBq. Apart from the pituitary gland, whichwas estimated to receive an absorbed dose of 0.19 mGy/MBq, the liver wasthe organ with the highest absorbed dose (0.16 mGy/MBq), followed by thekidneys (0.14 mGy/MBq).

TABLE 2 Organ Normalized Cumulated Activity Mean (MBq h/ SE (MBq h/Source organ MBq) MBq) Adrenals 2.65E−02 1.19E−02 Gallbladder 1.50E−026.71E−03 Lower large intestine 9.74E−02 4.36E−02 contents Smallintestine contents 5.23E−01 2.34E−01 Kidneys 4.78E−01 2.14E−01 Liver3.33E+00 1.49E+00 Muscle 4.23E+00 1.89E+00 Pancreas 9.40E−02 4.20E−02Red Marrow 3.59E−01 1.60E−01 Spleen 2.40E−01 1.07E−01 Urinary bladdercontents 1.10E−01 — Remainder 7.23E+00 3.23E+00

TABLE 3 Absorbed Doses Mean* Target organ absorbed dose (mGy/MBq)Adrenals 1.37E−01 Brain 1.27E−02 Breasts 1.32E−02 Gallbladder wall3.96E−02 Lower large intestine wall 4.32E−02 Small intestine 6.55E−02Stomach wall 1.93E−02 Upper large intestine wall 2.18E−02 Heart wall1.86E−02 Kidneys 1.39E−01 Liver 1.61E−01 Lungs 1.67E−02 Muscle 1.90E−02Ovaries 1.92E−02 Pancreas 9.27E−02 Red marrow 2.65E−02 Osteogenic cells3.35E−02 Skin 1.22E−02 Spleen 1.15E−01 Testes 1.36E−02 Thymus 1.49E−02Thyroid 1.41E−02 Urinary bladder wall 3.70E−02 Uterus 1.89E−02 Totalbody 2.50E−02 *Mean of 5 patients. Effective dose (mSv/MBq) was3.15E−02.

Comparative Lesion Detection

In an organ-based comparison of the 2 SRI modalities, 64Cu-DOTATATE PETdetected additional lesions in 6 of 14 patients (43%). All lesionsdetected on 111In-DTPAoctreotide SPECT were also detected on64Cu-DOTATATE PET. In 5 patients, the additional lesions were localizedin organs or organ systems not previously recognized as metastaticsites: lung lesions (patient 1), a single-bone metastasis and hepaticlesions (liver lesions were known from previously performed CT; patient8), bone metastases and lymph nodes (patient 9), peritonealcarcinomatosis (patient 12), pancreatic and pulmonary lesions (pulmonarylesions were known; patient 13), and a brain metastasis and asingle-bone lesion (patient 14). All foci detected by 64Cu-DOTATATE PETbut not by 111In-DTPA-octreotide SPECT were retrospectively assessed asbeing true-positive lesions, with the exception of the bone lesions inpatients 9 and 14. Thus, in these 6 patients, one or more of theadditional lesions found by PET were confirmed. 64Cu-DOTATATE PETrevealed in general more lesions (n>219, including 98 lymph nodes) thanconventional SRI (n>105, including 29 lymph nodes). A common feature ofnearly all additionally discovered lesions was their diminutive size(FIG. 2).

Table 4 gives a more detailed overview of the results from the findingsof the 2 SRI modalities, coregistered diagnostic CT, and follow-upimaging. FIG. 3 shows the pancreatic lesions of the patient known withmultiple endocrine neoplasia type I syndrome (patient 13) on a64Cu-DOTATATE PET/CT slice and on an equivalent contrast-enhanced latearterial-phase CT slice obtained 6 mo later. FIG. 4 illustrates thecerebral lesion of patient 14 seen on 64Cu-DOTATATE PET but not on111In-DTPA-octreotide SPECT.

TABLE 4 Number and Localization of Lesions Detected by Different ImagingMethods ¹¹¹In-DTPA-octreotide Patient no. SPECT ⁶⁴Cu-DOTATATE PET CTFollow-up* 1 Peritoneal carcinomatosis, Peritoneal carcinomatosis,Peritoneal carcinomatosis, bones (1), lymph nodes (8) bones (>10), lymphnodes bones (1), lymph nodes (>30) + lungs (6)^(†) (>25), lungs (1)^(†)2 Negative Negative Negative 3 Large solitary peritoneal Large solitaryperitoneal Large solitary peritoneal soft-tissue mass (1) soft-tissuemass (1) soft-tissue mass (1) 4 Negative Negative Negative 5 Lymph nodes(9) Lymph nodes (>30) Lymph nodes (10) 6 Liver (6), large solitaryperitoneal Liver (>10), large solitary Liver (2) soft-tissue mass (1)peritoneal soft-tissue mass (1) 7 Pancreas (1), liver (>10), Pancreas(1), liver (>10), Pancreas (1), liver (>10), bones (5) bones (>10) bones(1) 8 Breasts (>10), large solitary Breasts (>10), large solitaryBreasts (>10), large Bones^(†) peritoneal soft-tissue mass (1),peritoneal soft-tissue solitary peritoneal lymph nodes (1) mass (1),lymph nodes (18) + soft-tissue mass (1), liver (>10)^(†) + bones (1)^(†)hymph nodes (12) + liver (2)^(†) 9 Liver (1), large solitary peritonealLiver (1), large solitary peritoneal Liver (1) Lymph nodes^(‡)soft-tissue mass (1) soft-tissue mass (1) + bones (3)^(†) + lymph nodes(2)^(†) 10 Lymph nodes (8) Lymph nodes (10) Lymph nodes (4) 11 Liver(>10) Liver (>10) Liver (>10) 12 Ileum (1), liver (>10), bones (4),Ileum (1), liver (>10), bones (7), Ileum (1), liver (>10), Peritoneallymph nodes (2) lymph nodes (6) + Peritoneal lymph nodes (4)carcinomatosis^(†) carcinomatosis^(†) 13 Lymph nodes (1), Lymph nodes(1), thyroid gland Lymph nodes (3) + Pancreas^(†) thyroid gland (1)(1) + pancreas (3)^(†) + lungs (4)^(†) lungs (10)^(†) 14 Liver (1),large solitary peritoneal Liver (1), large solitary peritoneal Liver(1), large solitary Brain^(‡) soft-tissue mass (1), peritonealsoft-tissue mass (1), peritoneal peritoneal soft-tissue carcinomatosiscarcinomatosis + brain (1)^(†) + mass (1), peritoneal bones (1)^(†)carcinomatosis *Confirmation by follow-up with CT (coregistered,stand-alone). ^(†)Additional findings detected by PET method. ^(‡)Bonelesions in patients 9 and 14 have not been confirmed yet. If lesionswere known from previous investigations, confirmation was not demanded(Table 1). Besides abdominal SPECT, thoracic SPECT was performed inpatients 1, 5, 7, 8, 10, 11, 13, and 14, Numbers are given inparentheses.

The inventors found that PET with 64Cu-DOTATATE provided considerablybetter image quality than SPECT with 111In-DTPA-octreotide, resulting ina higher lesion detection rate for 64Cu-DOTATATE PET than for111In-DTPA-octreotide SPECT. In 5 patients (36%), 64Cu-DOTATATE PETrevealed lesions in organs not previously known as metastatic sites.This finding is of special interest because it may lead to more accuratestaging, which in turn may critically affect the therapeutic managementof NET patients. In no case did 111In-DTPAoctreotide SPECT detectlesions that were not also detected by 64Cu-DOTATATE PET. Organ-specificabsorbed dose estimates are given in Table 3. On the basis of thedosimetry data for the 5 patients, 64Cu-DOTATATE PET was associated witha lower radiation dose than after a standard administered activity of111In-DTPA-octreotide.

Despite known shortcomings and the limited number of patients, thisresult can be considered rather robust. Applying tissue-weightingfactors according to IRCP 60 and given the 200-MBq injected activity, wecan determine that 64Cu-DOTATATE delivered an estimated effective doseof 6.3 mSv to the patients, compared with 12 mSv for111In-DTPA-octreotide for a standard administered activity.

Conventional SRI with 111In-DTPA-octreotide usually follows a 2 dprotocol. In contrast, the time required for SRI is considerably reducedwhen using 64Cu-DOTATATE because of the accelerated imaging proceduresoffered by the physical and pharmacokinetic features of this tracer.

As shown herein, image acquisition can be initiated at 1 h afteradministration of 64Cu-DOTATATE. High spatial resolution was illustratedby sharp images, allowing for distinct delineation of small organs withappreciable somatostatin receptor expression such as the adrenals andthe pituitary. High image contrast could be demonstrated by notably highTBRs, even in organs with physiologic high somatostatin receptor densitysuch as the pancreas. In accordance with this is the detection of anadditional pancreatic lesion (TBR, 6:1) in patient 13 with knownmultiple endocrine neoplasia type I syndrome.

Despite enhanced clinical awareness and a consecutive diagnosticexploration by endoscopic ultrasonography, validation of the lesionshown on PET was not achieved until 6 mo later by contrast-enhanced CT,demonstrating a lesion size of 6 mm. Obvious advantages of PET systems,such as enhanced photon sensitivity and reduced acquisition times, havepaved the way for the clinical implementation of positron emitter-linkedsomatostatin analogs. Furthermore, the spatial resolution achievable byPET is generally higher than that by SPECT. However, a limiting factorfor high-resolution PET is the positron energy of the used isotope.

The use of isotopes with a lower positron energy is therefore consideredadvantageous and may result in reduced image blurring because ofcorrespondingly shorter positron ranges. That impact is considered to bemodest in human state-of-the art whole-body PET scanners with intrinsicspatial resolution on the order of 4-6 mm in full width at half maximum.However, the impact of positron energy may become more decisive as PETscanner technology continues to advance.

The invention claimed is:
 1. A method of diagnosing a neuroendocrinetumor in a radiographic imaging method, the method comprising contactingcells or tissues with a compound of Formula I or a pharmaceuticallyacceptable salt thereof

wherein the compound is administered with a target dose in the range of150-250 MBq, and making a radiographic image for detecting the compound.2. A method of claim 1, wherein the compound is administered with atarget dose in the range of 191-210 MBq.
 3. A method of claim 1, whereinthe compound is detected by a gamma camera, positron emission tomography(PET), or single photon emission tomography (SPECT).